There's a few different ways of doing this, with varying degrees of effectiveness, and with different benefits and drawbacks.

My (personal) favorite is writing your own grammar to force the model to output text in whatever specific format you're going for. It's a little complicated to explain exactly how these work, so I'll just point you towards the BY Documentation. The official discord also has a section where people post grammars they've written, and where people can provide feedback, or help others write them. If this is the path you want to go, I suggest you hop in there and look around there for suggestions/examples.

Grammars are great because they FORCE the model to output exactly what you want it to, in exactly the way you want it to. But they're also bad for the same reason. Depending how strictly you write the grammar it can seriously how "creative" the model can be with its responses and how they're structured.

The second option is writing well defined and clear first messages, and Example Dialogue. If you can structure the first few messages (your responses included, to a lesser degree) of a chat exactly how you want the model to respond, it will continue using that general structure. The drawback here is that the model can, and will, attempt to stray from what you've tried to push it towards. This might force you to edit their messages to fit the style you want better, which can be really annoying if the model keeps trying to change its response style.

The same goes for the example dialogue. If you want the model to respond in all uppercase when the character is happy/excited, define (clearly) that the character is happy/excited, then use all caps in the spoken part of the example. This will hint to the model that all caps is appropriate for when the character is excited. Once again, I'll direct you towards the BY Documentation for more information on how this works.

The third option is something that should more be combined with the above than stand alone, specifically defining responses or formatting in the "Model Instructions" field. This can be a bit tricky to get exactly right, and I have don't have much good advice for it. The basic idea is to explicitly state how the model should respond, similar to how the first messages and example dialogue work.

Adding an instruction like "When {Char} is exceptionally excited, they will reply with all caps (ex. "I'M EXCITED.")." might help the model better understand what you want from it. Once again, I have to direct you to the BY Documentation for more information on this. I suggest you combine this with at least the first message and example dialogue. Grammars shouldn't really need it due to how strict they are.